Process for deep-fat cooking

ABSTRACT

A new process for the continuous deep-fat cooking of a food to produce a processed comestible wherein the food is passed through an elongated cooking zone. Hot cooking oil is introduced and withdrawn from the cooking zone at a plurality of points to produce hydraulic effects which insure proper contact of the food with the cooking oil. 
     Said cooking oil is continuously flowed upwardly through a plurality of spaced points dispersed over the entire bottom surface of the entrance end of the cooking zone and continuously withdrawn downwardly downstream therefrom. Withdrawn oil may be reintroduced directly without being reheated at a point downstream of the point of withdrawal in addition to being recycled to the source of heated cooking oil.

This is a continuation of application Ser. No. 363,379, filed May 24,1973 and now abandoned which, in turn, is a division of application Ser.No. 108,303, filed Jan. 21, 1971, now U.S. Pat. No. 3,754,468.

This invention relates to a new process for the cooking of foods, andmore particularly to a new process for the deep-fat cooking of foods toproduce processed comestibles, such as potato chip and like products.

BACKGROUND OF THE INVENTION

Early processes for continuously deep frying potato slices and the liketo produce potato chips utilized elongated cooking troughs or kettlescontaining a cooking oil which was heated by the direct contact of hotgases with the underside of the kettle bottom. Potato slices and otherlike materials to be processed were floated along the surface of thecooking oil and pushed throughout the length of the kettle byspaced-apart pusher assemblies.

More recent processes employed elongated troughs or kettles wherein thecooking oil was separately heated, either directly or indirectly e.g., aboiler or heat exchanger and passed to the cooking apparatus. A majorportion of the oil was introduced into the kettle at the slice-receivingend of the kettle, withdrawn from the other end, reheated andre-introduced into the kettle. With due consideration to heat transferrequirements, i.e., sensible heat required to raise the potato slice tocooking temperatures, latent heat required to vaporize the water contentof the slices, maximum temperature to which the cooking oil may beheated without excessive break down thereof to free fatty acids, etc.,in view of the cooking time required for an average size potato slice,it was necessary to provide mechanical restraining devices, such asrotating flow wheels, rakes or submerger belts, intermediate the ends ofthe kettle to provide the necessary residence time for dewatering thepotato slices (about 80% by weight of the slice) and for cooking thepotato slices. This resulted in an oil flow rate through the kettle ofabout 5 to 6 times the rate of flow of the potato slices where aresidence time of from about 3 to 4 minutes is required to produce anacceptable product. Final cooking of the slice is generally thought tobe the reduction of the water content from about 10% to about 2% whichis the moisture content of an acceptable product.

In many of the prior art apparatus, the potato slice had a tendency toadhere to the surface of the kettle as well as to the mechanicalrestraining devices in the early stage of cooking when the potato sliceis in a pliable plastic state causing a dam effect thereby resulting inthe development of areas of high cooking oil velocities in the clearancebetween the restraining mechanisms and the bottom and sides of thekettle. Some slices would surge through the areas of such high velocityand would not be retained in the kettle for a time sufficient to beproperly cooked. Such high velocities of cooking oils created by thedamming effect also had a tendency to develop eddies or whirlpools whichwould excessively restrain some of the slices being processed to theextent that the resulting chip was overcooked, and in some instancesburnt thereby requiring manual removal prior to packaging. Breakage ofan overcooked or burnt chip would result in fines in the cooking oil andfines in the cooking oil tend to break down the oil and form free fattyacids which are detrimental to the flavor and shelf life of the product.Additionally, high heat levels required at the inlet end necessitatehigh oil flow rates to provide for proper heat levels for final cookingof the slice.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a new process for thedeep-fat cooking of foods to produce processed comestibles, such aspotato chips and like products.

Another object of the invention is to provide a new process for thedeep-fat cooking of foods which will reduce cooking times and form amore uniform product.

Still another object of the invention is to provide a new process forthe deep-fat cooking of foods whereby improved thermal efficiencies areachieved.

A further object of the invention is to provide a new process for thedeep-fat cooking of foods which will reduce cooking oil requirements perunit weight of product than heretofore achieved.

A still further object of the invention is to provide a new process forthe deep-fat cooking of foods which will substantially reduce thequantity of fines produced.

These and other objects of the invention are achieved in an elongatedtrough or kettle wherein a major portion of the cooking oil isintroduced into the kettle at the food-receiving end over a large areain essentially countercurrent contact to the food slices beingintroduced into the kettle. The food slices initially fall towards thebottom of the kettle but are caused to move gently upward by thehydraulic force of the rising cooking oil which helps to separate thewet slices as the violent boiling action is initiated by the formationof water vapor. The slices pass into a second zone of the kettleincluding an agitating means and a means for introducing a secondportion of heated cooking oil from a plurality of points above thesurface of the cooking oil which effects another hydraulic force tocause the slices to tumble to insure that all surfaces are properlyexposed to the cooking oil. In this second zone, a portion of thecooking oil is withdrawn and passed to a subsequent zone. The slicesmove to a third zone wherein the final cooking thereof is effected atcontrolled cooking oil temperatures most effective for completion of thecooking process. In the third zone, the slices are subjected to afurther hydraulic effect by the introduction of cooking oils withdrawnfrom the second zone. By the continuous introduction into the kettle ofcooking oils at controlled temperatures and flow rates in accordancewith the present invention, the cooking time of the slice may be reducedby as much as 33% with an increase in capacity for a given kettle sizeby as much as 58% per square foot of surface area compared with priorart processes. The concentration of slices in the cooking oil results inwhat may be called a slurry which is dense enough for essentially plugflow thereby producing a more uniform product.

Since the oil turnover rate, i.e., oil absorbed into the slices, isincreased by the greater production rate in a like size kettle whichreduces the length of time oil remains in the system, the tendency ofthe oil to break down and form free fatty acids is reduced which permitsthe preparation of a product having a longer shelf life. Additionally,the hydraulic effects produced in accordance with the invention achieveimproved heat transfer relationships between the slices and cooking oilssince temperature gradients at any given cross-sectional point in thekettle are minimized as compared to prior art apparatus whereintemperature stratification due to the damming effect was commonplace.For ease of understanding, the invention will be described withreference to the treatment of potato slices to produce potato chips, itbeing understood that other foods suitable for deep-fat cooking may bealso used. It will be appreciated from the following description of theinvention that the temperature of the hot oil at various points in thekettle may be controlled to any necessary degree by the valvingarrangement to permit mixing of oil streams at different temperaturelevels to achieve temperature levels proper for the treatment beingeffected, i.e., initial evaporation of a portion of the water content ofthe slice, and cooking. It is understood that not all of the watercontent is eliminated from the processed comestible.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention will become apparentupon consideration of the detailed disclosure thereof, especially whentaken with the accompanying drawings wherein like numerals designatelike parts throughout:

FIG. 1 is a schematic side sectional view of the apparatus of theinvention and a schematic flow diagram of the process for the deep-fatcooking of foods;

FIG. 2 is a sectional top view of the apparatus partially schematictaken along the lines 2--2 of FIG. 1; and

FIG. 3 is an enlarged cross-sectional view of the receiving end of theapparatus taken along the lines 3--3 of FIG. 2.

Referring now to the drawings there is illustrated a cooking apparatus,generally indicated as 10, comprised of an elongated trough or kettle 12suitably sheathed with heat insulating material (not shown) having areceiving end and a delivery end, generally indicated as R and D,respectively. The surface level of the cooking oil and product beingprocessed in the kettle 12 is indicated as L. The top of the kettle 12is partially enclosed with a hood 14 having a vent 16. A deflector plate18 for condensate removal is suitably mounted (not shown) with the hood14 below the vent 16. Within the receiving end R of the kettle 12, thereis positioned an oil distribution means, generally indicated as 20,comprised of a plate 22 having a plurality of orifices and forming anoil distribution zone 23 with the bottom and side walls of the kettle12. The angle of the plate 22 may be varied by an adjusting means (notshown) depending on desired cooking conditions, as more fullyhereinafter discussed. Below the plate 22, the bottom of the kettle 12is provided with a oil inlet manifold 24 (See FIG. 3). Downstream of thedistribution plate 22, weirs 26 are provided extending crosswise to thelength of the kettle 12.

A chip agitator means, generally indicated as 28, is providedintermediate the ends R and D suitably mounted to a drive assembly (notshown) to effect a vertical reciprocating motion. The chip agitator iscomprised of plurality of horizontally extending bars 30 mounted to anupper support member 32 by a plurality of hangers 34. Below the uppersupport member 32 and above the surface of the cooking oil L, there isprovided an oil distribution means, generally indicated as 40, comprisedof an inlet manifold 42 extending across the kettle 12 with a pluralityof longitudinally extending conduits 44 having orifices therein (notshown) suitably mounted thereto. Below the oil distribution means 40,the bottom of the kettle is formed with a perforated plate 46 forming anoil collection zone 48 with a bottom plate 50, triangularly shaped sidewalls 52 and a front wall 54 (See FIG. 3). The front wall 54 is providedwith an outlet manifold 56.

Between the chip agitator means 28 and the delivery end D of the kettle12, there is provided a rake means, generally indicated as 60, of adesign known to those skilled in the art, such as that illustrated inU.S. Pat. No. 2,085,494 to Joseph D. Ferry, entitled "Impeller Mechanismfor Cooking Apparatus". The rake means 60 is comprised of a plate 62having a plurality of orifices (not shown) formed therein and aplurality of downwardly extending fingers or prongs (not shown) affixedto the bottom. The plate 62 is mounted to a support assembly 64 bysupport bars 66 and is caused to move in an oval or elliptical path by adrive means (not shown) with movement being essentially clockwise to theaxis of the rake means 60 when viewing FIG. 1. Positioned above theperforated plate 62 there is provided a fluid distribution means,generally indicated as 68 comprised of a troughed plate 70 having aplurality of perforations, and a manifold 71 having conduits 72extending downwardly therefrom to a point above the troughed plate 70.Below the chip delivery end D and at the bottom of the kettle 12, thereis provided an outlet manifold 75.

Above the receiving end R of the kettle 12, a feed conveyor 76 ispositioned for introducing the slices into receiving end R. Positionedabove the conveyor 76 is a slice separator, generally indicated as 77comprised of a cylinder 81 having a plurality of flexible extensions orfingers 83. The slice separator is caused to rotate clockwise by a motormeans (not shown) at a rotational velocity greater than the linearvelocity of the belt of conveyor 76 to separate the slices to reduce thenumber of chips withdrawn from the kettle having soft centers. Thedelivery end D is provided with a discharge conveyor 78 having aplurality of outwardly extending fingers or prongs 79 which assist inremoving the chips from the kettle 12. The assemblies for forming potatoslices from whole potatoes (i.e., washer, peeler, slicer, etc.) and forpackaging the potato chips do not constitute a part of this inventionand are of the type presently known and used by those skilled in theart.

Referring now to FIG. 1 wherein there is illustrated a schematic flowdiagram of the invention, the major components thereof include inaddition to the cooking apparatus 10, a heater 80, an oil storage tank82, a strainer tank 84, and a liquid leveling device 86. The heater 80is in fluid communication by line 90 and line 92 under the control ofvalve 94 with inlet manifold 24, and by line 90 and line 96 under thecontrol of valve 98 with the oil distribution means 40. The outletmanifold 56 of the kettle 12 is in fluid communication through line 100by pump 102 and line 104 with inlet manifold 71 by line 106 under thecontrol of valve 108. The outlet manifold 75 is in fluid communicationby line 110 with strainer tank 84 wherein fines are removed from thecirculating oil. The strainer 84 is connected by line 112 and pump 114to heater 80 through line 116.

The liquid leveling device 86 is in fluid communication with kettle 12by line 118. The storage tank 82 provides a source of oil to levelingdevice 86 through line 118 by pump 120 and acts as a surge tank forlevel device 86 by line 122. Lines 104 and 110 are in fluidcommunication therebetween by line 124 under the control of valve 126for adjusting heat requirements, as more fully hereinafter discussed.

In operation, hot cooking oil at a temperature of from about 335° to370° F. is introduced into the kettle 12 through the manifold 24 intothe zone beneath the plate 22 from heater 80 by lines 90 and 92. Theheater 84 is illustrated as being of the direct fired type; however, itis understood that a heat exchanger may be employed wherein the cookingoil is heated by indirect contact with an intermediate heat transferfluid.

Potato slices are passed to the kettle 12 by conveyor 76 from which theslices drop into the receiving end R of the kettle 12 and contactcountercurrently the hot cooking oil passing upwardly through theorifices of plate 22. As mentioned above, the angle of the plate 22 maybe varied dependent upon the material being treated, residence time,cooking temperatures, and the like. After the initial impact of theslices into the cooking oil, the slices are agitated by the upwardhydraulic effect of the cooking oil being introduced over a wide areawhich effect help to separate the wet potato slices as the violentboiling action caused by water vapor being released from the slices. Asis known to those skilled in the art, the greatest heat requirements areduring the initial contact of the potato slices with the cooking oilwhen 25% of the moisture of the potato slice is removed and is easilyachieved by the present invention. This initial treatment will behereinafter some time referred to as "phase I cooking".

The potato slices will form a bed, generally of from 3 to 4 inches ormore which moves continuously towards the discharge end D of the kettle12. The slices and hot cooking oil pass over the weirs 26 which togetherwith the effect of the vertical reciprocating movement of the bars 30 ofthe agitator 28 further cause the slices to tumble to assure exposure ofall surfaces of the slices to the cooking oils. As the bed of slicesmoves into the intermediate portion of the kettle 12, the bed iscontacted with an additional quantity of cooking oil in the form of aplurality of streams thereof from the liquid distribution means 40. Thestreams of cooking oils provides another hydraulic effect to tumblefurther the slices to expose all surfaces of the slices to the cookingoil. As mentioned hereinabove, such hydraulic effects minimize adherenceof the slices to the surface of the kettle and to each other when theslices are in a pliable plastic state.

A portion of the cooking oil introduced into the kettle from the heaterby line 90 is withdrawn from kettle 12 through perforated plate 46 viaoutlet manifold 56 and is passed through line 100 by pump 102 forsubsequent use as more fully hereinafter described. During passage ofthe bed of slices through the intermediate section of the kettle 12further dewatering of the slice is effected and such passage willhereinafter some time be referred to as "phase II cooking".

The bed of slices thereupon pass into the last section or zone of thekettle 12 wherein completion of the cooking of the slices is effected,hereinafter some time referred to as "phase III cooking". The rotationalmovement of the rake means 60 is such to effect an essentiallyelliptical movement of the rake plate 62 whereby the fingers or prongsthereof dip into the bed of slices, move to the left (FIG. 1) and thenelevated from the surface of the material and returned to the startingpoint (essentially a clockwise movement). During this essentiallyleftward movement, the fingers or prongs engage and move the slices,thus assisting the oil flow in traversing the slices through phase IIIcooking. Additional cooking oil in line 106 is supplied by manifold 71through conduits 72 onto the trough plate 70 from which the oil passesthrough the orifices onto the rake plate 62 and thence to said oil-slicebed through the orifices therein. It will be noted that a portion or allof the cooking oil introduced onto the plate 70 is the cooking oilremoved from the kettle 12 in line 100. The now-cooked slices or chipspass to the delivery conveyor 76 whereat the prongs or fingers 79affixed to the conveyor belt of the conveyor 78 assist in withdrawingthe chips from the cooking oil. Cooking oil in discharge end D iswithdrawn from manifold means 75 and passed by line 110 to strainer 84wherein fines are removed. The cooking oil is withdrawn from strainer 84in line 112 by pump 114 and is passed through line 116 to heater 80wherein the cooking oil is raised to the required temperature level forre-introduction into the kettle 12.

The oil leveling device 86 is connected to a remote sensing device (notshown) which measures the level of cooking oil and slices in the kettle12. The leveling device 36 is in fluid communication with storage tank82 (continuously or discontinuously) by pump 120, i.e., pumpcontinuously running or activated in response to a signal from theremote sensing device. Should the remote sensing device be activated inresponse to a level below the preselected level L, cooking oil isintroduced into the kettle 12 by line 118 from storage tank 82 under thecontrol of the leveling device 86 until the preselected level L isreached, at which point the fluid flow through the line 118 isdiscontinued.

It will be appreciated from the conduit and valving arrangement that thetemperature of the oil may be controlled to any necessary degree toprovide control of the oil temperature within the kettle 12 at the mosteffective temperature level for accomplishing the desired purpose in thevarious cooking phases. For instance, there are greater heatrequirements in phase I cooking wherein the temperature of the slices isfirst raised to 212° F. at which point the water contained in the slicesbegins to vaporize and wherein vaporization of water in the slices iseffected to the extent that approximately 25% thereof is removed. A hightemperature level of the cooking oil is desirable for phase II cookingwherein the slices are further dewatered whereas lower temperaturelevels of the cooking oil for phase III cooking is generally preferredparticularly from the standpoint of the color of the final product. Forinstance, with potato slices having a high sugar content, it isdesirable to have a low temperature level in phase III cooking toprevent overcooking (excessive carmelization of the sugar) whereby adark brown product results. Thus, the temperature level in phase IIIcooking is varied by proportioning the flow of cooking oil withdrawn inline 100 between lines 106 and 124. For higher temperature levels, theratio between the flow of cooking oil in line 108 to line 124 isincreased whereas for lower temperature levels the ratio is decreased.It is understood that all of the cooking oil withdrawn in line 100 fromkettle 12 may be passed to the phase III cooking stage.

The term "countercurrent contact" is used to described the relationshipbetween the direction of flow of the chips into the kettle 12 and thedirection of flow of cooking oil being introduced into the zone in whichchips and oil contact therebetween; i.e., greater than 90°.

Operation of the process and apparatus is described in the followingspecific example which is intended to be merely illustrative and theinvention is not to be required as limited thereto.

EXAMPLE I

Potato slices having a 20.0% solids content were introduced at a feedrate of 2540 pounds per hour into a kettle 29 feet long and 1 foot wide.Cooking oil at a temperature of 358° F. was introduced at the rate of177 GPM and 73 GPM into the kettle through lines 92 and 96,respectively. The desired residence time for the potato slices beingtreated was determined to be between 150 to 180 seconds. Cooking oil ata temperature of 326° F. was withdrawn at the rate of 200 GPM and passedto manifold 71. Cooking oil at a temperature of 314° F. was withdrawn atthe rate of 250 GPM from kettle 12 through outlet manifold 75. Thepotato chips withdrawn from the kettle 12 by the conveyor 78 hadexcellent color and taste.

It will be understood that the ability to alter the angle of the baffleplate 22 with the resultant alteration of the hydraulic effect of thecooking oil is one important factor in controlling the flow rate of thechips for proper residence time for cooking the slices which isdependent on various considerations including age of the potato afterharvest. The process and apparatus of this invention provides thecontrol of and assurance of proper temperature levels to suit therequirements of the local market under varying conditions of the potatoslices being treated. It will be appreciated that by reducing thevelocity of the cooking oil through the kettle essentially eliminatesthe whirlpools and eddy currents of the prior art apparatus and theirdeleterious effect.

Numerous modifications and variations of the invention are possiblewithin the above teachings and therefore the invention, within the scopeof the appended claims, may be practised other than as particularlydescribed.

We claim:
 1. In a continuous process for cooking comestibles in cookingoil in an elongated cooking area defined by an entry end, an exit end,and a horizontally elongated body of heated cooking oil continuouslyflowing horizontally from adjacent said entry end to said exit end, andhaving a separate source of heated cooking oil, the steps whichcomprisea. segregating said body into first and second cooking zones byan area of restricted horizontal flow; b. continuously flowing heatedcooking oil from said source upwardly at a plurality of spaced pointsdispersed over the entire bottom surface of said first cooking zone toeffect a generally vertical upward flow of cooking oil over the entiresaid first cooking zone; c. simultaneously with said flowing step,continuously introducing comestibles into said first zone, saidcomestibles falling through said upwardly moving oil from said flowingstep; d. comingling said cooking oil and said comestibles in said firstzone for the cooking thereof and causing moisture removal therefrom,whereby said comestibles become buoyant in said cooking oil; e.continuously moving horizontally said partially cooked now floatingcomestibles through said area of restricted flow to said second cookingzone by hydraulic action of horizontal flow of upper portions of saidbody of oil from said first zone; f. continuously cooking saidcomestibles in said second zone as they are moved therethrough by saidhorizontally moving body of oil; g. continuously removing saidcomestibles from said exit end; and h. continuously withdrawing cookingoil from said exit end for the recycling thereof to said source.
 2. Theprocess of claim 1, further characterized bya. continuously introducingin a second flowing step cooking oil from said source verticallydownwardly over and through said continuously horizontally movingcomestibles and cooking oil, said second flowing step being downstreamof said area of restricted horizontal flow and at a plurality of pointsdispersed over the surface thereof; b. continuously withdrawingdownwardly a portion of said horizontally moving body of cooking oildownstream of said area of restricted horizontal flow; and c.reintroducing directly without reheating said withdrawn portion to saidbody at a point downstream of the point of withdrawal.
 3. The process ofclaim 2, further characterized bya. said reintroducing step beingcarried out by said withdrawn portion introduced above the surface levelof said horizontally flowing body at spaced points thereover.
 4. In acontinuous process for cooking comestibles in cooking oil in anelongated cooking area defined by an entry and, an exit end and threesequentially spaced cooking zones, and having a separate source ofheated cooking oil, the steps which comprisea. continuously flowing, ina first flowing step, heated cooking oil from said source upwardlyadjacent the entry end of said cooking area at a plurality of spacedpoints dispersed over the entire bottom surface of said first cookingzone to effect a generally vertically upward flow of cooking oil in saidarea, said first cooking zone being partially segregated from saidsecond cooking zone; b. simultaneously with said first flowing step,continuously introducing comestibles into said first zone adjacent saidentry end, said comestibles falling through said upwardly moving oilfrom said first flowing step; c. comingling with said cooking oil andsaid comestibles in said first zone for a first phase cooking thereof,causing moisture removal therefrom, whereby the comestibles becomebuoyant in said cooking oil; d. continuously moving upper portionslayers of said cooking oil from said first flowing step horizontallyfrom said segregated first cooking zone over a weir to said secondcooking zone; e. continuously moving said partially cooked now floatingcomestibles from said first zone to said second zone by hydraulic actionof said horizontally flowing oil; f. continuously introducing in asecond flowing step cooking oil from said source downwardly over andthrough said continuously horizontally moving comestibles and cookingoil in said second zone from a plurality of spaced points above thesurface thereof for a second phase cooking of said comestibles in saidsecond zones; g. simultaneously with said second flowing step,continuously withdrawing in a first withdrawing step cooking oildownwardly from the bottom of said second cooking zone; h. introducingdirectly without reheating said cooking oil from said first withdrawingstep downwardly over and through said continuously horizontally movingcomestibles and cooking oil in said third cooking zone at spaced pointsabove the surface thereof for a third phase cooking thereof; i.continuously removing comestibles from the exit end of said cooking areaafter the third phase cooking thereof; and j. continuously withdrawingin a second withdrawing step cooking oil from the exit end of saidcooking area for the recycling thereof to said source of heated cookingoil.